KR20000005257A - Metal continuous casting method and ingot mold for conducting - Google Patents

Abstract

PURPOSE: An ingot mold is provided to guarantee effective reduction of heat flux discharged at the initial growing of a solidified surface and to prevent the level of the free surface from shaking. CONSTITUTION: The ingot mold has a device such as heat conductive metal covering layers(6,15) that is lower than a wall for reducing heat current speed discharged from a casting metal(2), or a metal wall installing a groove(31) in the wall, that is cooled by force. A insulating cropping element related to the gas injecting device that ends a distributed nozzle on the inner edge face of the ingot mold, is provided in the upper part of the wall. The device is used for a steel continuous casting by solidifying a solid surface part(21) on the upper part of the metal wall and maintaining the free surface of a liquid metal among the casting in the same level as the cropping element.

Description

Ingot mold for continuous casting of metals and their implementation

The present invention relates to continuous casting of metals, in particular steel.

Continuous casting operations, as is well known, consist schematically of pouring molten metal into an ingot mold defining a passage of the casting metal, which consists mainly of a tubular element without bottoms, but here it is made of copper (usually made of copper alloy). The wall of the manufactured ingot mold is forcibly cooled by the circulating water, and the product which has already solidified outside is continuously drawn out of the ingot mold mold. The solidification then proceeds towards the center of the product and is completed in the so-called "second cooling" zone under the influence of the water spray line during the descent of the product downstream of the ingot mold. Next, the obtained product (bloom, billet or slab) is cut and rolled to a predetermined length or transformed into bars, wires, sections, plates, sheets or the like before being transported to the consumer.

Surface defects or subsurface defects of the product obtained by continuous casting of steel may lead to scrapping if not well tolerated by rolling or to an unacceptable degree of metallurgical quality of the rolled product. You may.

During casting, molten metal injected into the ingot mold forms a solid film at the free surface level of the metal when it comes into contact with the cold metal of the ingot mold. This membrane is driven downward by a jerky movement interrupted by the vertical vibration of the ingot mold during withdrawal of the product. At the same time, its thickness increases due to continuous heat release through the walls of the ingot mold. Thus, a new film of solid metal is created continuously at the level of the free surface of the metal in the ingot mold, which film is spherical and prone to shrinking due to solidification over the entire boundary of the inner wall of the ingot mold and thus cooling while descending from the ingot mold. It consists of a ring.

The heat shrinkage of the solid skin is large when heat dissipation increases, for example by the natural tendency of the cast metal to shrink during cooling by changes in the solid phase at the end of solidification, in which case low carbon steel or medium carbon steel or stainless steel grades. Especially applies to

This peripheral shrinkage separates the solidified skin from the wall of the ingot mold and thus leads to a reduction in heat exchange when the contact of the skin with the cooling wall is poor. This separation is generally not the same across the interface of the solidified epidermis and is the source of surface defects in the final product obtained.

In order to avoid or limit such defects, attempts have been made to reduce the heat flux released during the formation of the skin at the start of solidification.

Thus, attempts to reduce this heat flux have been made by using an ingot mold with an insert formed thereon that forms a thermal barrier that prevents molten metal from making direct contact with the cooling wall of the ingot mold. Already done However, the resistance to the time of such an insert is very irregular, and the maintenance cost of such an ingot mold is very expensive.

For example, ingots have a surface finish that reduces the area of the area where the cast metal is in direct contact with the copper of the cooling wall, by uniformly carving the walls forming the wafer pattern on these surfaces, or by irregular roughness obtained by, for example, sandblasting. Attempts have also been made to reduce the heat flux by making a wall of the mold. However, this method cannot yet significantly improve the surface quality of the cast product. In practice, the variation caused by the variation in the free surface level of the cast metal is dominant compared to the effect of ablation of the heat flux on the free surface of the cast metal obtained by surface finishing the wall of the ingot mold as described above, so that There is a nonuniformity, so that surface defects are not eliminated.

It has also been attempted to make vertical grooves in the wall, with the aim of reducing the direct contact between the cast metal and the cold copper of the wall again. However, these grooves are quickly filled with slag conventionally used as a layer covering the free surface of the liquid metal and it has been found that this reduces the desired thermal effect.

It is an object of the present invention to solve the above problems, in particular to ensure an effective reduction in the heat flux released during the formation of the solidified skin and at the beginning of growth and at the same time especially at the level of the free surface of the liquid metal in the ingot mold This ensures that casting products of very good quality are obtained while avoiding the adverse effects of fluctuations in the stiffness.

With this objective in mind, the present invention includes a metal wall that extends almost vertically and is forcibly cooled and defines a passage of the cast metal and releases the heat flux of the cast metal causing gradual solidification and cooling of the metal. A method of continuous casting of molten metal, especially steel, in an ingot mold that ensures that over its entire height, according to the method, the intensity of heat flux released near the level at which the metal begins to solidify in contact with the wall is reduced. A feature of this method is that while a thermally insulated rise frame is placed on the cooling metal wall and is cast, the level of the free surface of the cast metal is maintained within the frame and is distributed around the inner circumferential wall of the ingot mold. Gas in the form is injected at the level of this frame, preferably at its lower end.

According to the invention, the free surface (maniscus) of the liquid metal bath is located in the frame. The frame is made of a refractory insulating material, so that the solidified metal film starts to form uniformly only from the upper edge of the metal wall, which is a part of this desired uniform solidification on the cooling metal part from the undesired local solidification part which may occur in the fire part. Ensure correct separation. Thus, solidification of the cast metal is only initiated at certain intervals in the meniscus. As a result, this solidification initiation region is completely flat, horizontal and free of fluctuations or disturbances that inevitably disturb the free surface of the bath. The solid ring comprising the first solidified skin is geometrically completely uniform and the continuous regeneration of the ring upon lowering of the cast product is almost completely uniform in the same manner as the growth of this solidified skin.

In addition, solidification of the cast metal is not initiated in the frame so that the metal does not shrink at this level. The metal is in contact with the wall of the frame and prevents infiltration of slag between the metal and the wall. As a result, even when the skin portion is separated from the wall due to solidification shrinkage, there is no infiltration of slag between the metal wall of the ingot mold and the skin portion solidified at their contact portions. In addition, due to the height of the metal in the frame, the static pressure of the liquid metal suppresses this separation, thus keeping the skin part against the surface of the metal wall and the skin part is uniform around the entire inner circumference of the ingot mold and thus the table The thickness and coagulation of the skin are also uniform around it.

Thus, due to this circumference uniformity, heat dissipation performed at the top of the metal wall is also achieved in the same way around the entire interface of the product, avoiding local separation and thickness underestimation that may occur at the solid skin that will occur, The intensity of the heat flux released in the solidification initiation region can be ensured in much the same way around the entire boundary of the passageway defined by the metal wall.

Preferably, the intensity of the heat flux released does not significantly change the overall amount of heat released by the ingot mold but is reduced over a region of a predetermined height from the lower edge of the frame. This limited height thus ensures a reduction in the heat flux emitted in the area where the solid metal skin is formed and also avoids the influence of separation and rinsing of the metal skin that is observed in the casting process according to the prior art.

According to a first variant, the region has a rather constant heat flux release capacity with respect to its overall height. In this case, the reduction of the heat flux released can be high, for example for only small heights of 10 mm.

According to a second variant, the region has an increasing heat flux release capability from top to bottom. In this case, the decrease in the released heat plus gradually decreases towards the bottom of the ingot mold for the area with a large height. This allows for even greater reductions in the heat flux emitted than in the previous case in areas where this decrease is due to the large height of this region, and also allows the released flow rate to be as low as possible and the heat flux release to be maximum. A kind of graduality is ensured in the variation of the heat flux released between the cooling metal parts of the ingot mold under consideration.

The object of the present invention is also a continuous casting comprising a metal wall extending almost vertically and defining a passageway for the cast metal, and cooling means in the interior of the wall over their heights to ensure forced cooling of the wall. In the ingot mold, the wall having a means thereon for passing the inner surface of the wall defining the passageway and reducing the intensity of the heat flux caused by the cooling means, the ingot mold being disposed above the metal wall And a gas injection means passing into the inner circumferential wall of the ingot mold at the level of the frame, preferably at the lower end of the frame, directly above the metal wall.

According to a first configuration, said heat flux intensity reducing means comprises a metal layer having a lower thermal conductivity than the metal forming the wall, said metal layer comprising eg nickel deposited on the copper or copper alloy of the ingot mold wall by an electrolytic method. do.

According to a first variant, the layer is located above the wall, ie between the refractory material constituting the frame and the wall, the thickness of which may be for example about 1 millimeter.

According to another variant, the layer also extends above a height of about several centimeters with respect to the inner surface of the cooling metal wall. The poor conductive metal layer then forms a thermal barrier between the very good thermal conductive metal of the ingot mold wall and the solidification skin of the cast metal. With respect to the overall height at which this poor conductive layer extends, the heat flux released is greatly reduced (reduction can reach or even exceed 50%) when compared to the shape where the cast metal is in direct contact with the conductive metal of the wall. May be).

The formation of a poor conductive metal layer on the copper or copper alloy wall and on its inner side is dependent upon the simultaneous deformation of the mean value of the flow rate emitted from the top of the cooling wall and the distance from the top edge of the metal wall to the level at which the cast metal film starts to solidify. It is possible to precondition and facilitate this spread by enabling the spread of the flow rate and by gradually reducing the thickness of the layer from the government to the floor.

According to a second embodiment, said heat flux intensity reducing means comprises a groove made on the inner surface of said wall to extend somewhat vertically. Thus, in the region where the coagulation film is formed and with respect to the circumferential wall of the passage formed by the wall of the ingot mold, the portion where the cast metal is in direct contact with the copper or copper alloy of the cooling wall and heat dissipation is reduced. Corresponding parts alternately exist. Unlike the technique using the groove system mentioned earlier in the present specification, the start of solidification is, according to the invention, made below a certain distance of the free surface of the metal bath, ie away from the slag, so that the slag is infiltrated into the slot during casting. Will prevent the slots from being blocked.

According to a variant of the arrangement of this arrangement, the grooves are at least partially filled with a material having a lower thermal conductivity than the metal which forms the wall.

Other features and advantages will be apparent from the description of the continuous steel casting ingot mold according to the present invention.

Referring to the accompanying drawings:

1 is a schematic drawing of a first configuration variant, showing a partial longitudinal cross-sectional view of an upper portion of an ingot mold.

FIG. 2 is a diagram showing the change in distance from the upper edge of the metal wall to the heat flux released during casting in such an ingot mold.

3 and 4 are second configuration modifications of the ingot mold and correspond to FIGS. 1 and 2, respectively.

FIG. 5 is a schematic illustration of the top of an ingot mold wall for a second configuration using grooves in the upper section of the metal wall. FIG.

FIG. 6 is an enlarged horizontal cross sectional view through the top of the metal wall of FIG. 5; FIG.

FIG. 7 is a view similar to FIG. 6 and illustrates a case where a groove is filled with a weak metal.

8 shows a particularly effective frame configuration with a thermal resistor.

9 is a schematic cross-sectional view of a reduced scale of an ingot mold taken along the line VIII-VIII in FIG. 8.

The ingot mold shown in FIG. 1 has a metal wall 1 which is cooled in an originally known manner by the internal circulation of water, which forms a tubular body and defines a vertical passage for the cast steel 2. . The upper part of this metal wall is preferably made of copper or copper alloy, for example in the form of a ring-shaped part 3, and is separate from the lower part with a self-cooling circulation device schematically shown in the water circulation channel 4. It is made of components.

This ring-shaped portion 3 can be easily replaced at a lower cost than the metal wall is formed in a single part with respect to its entire height.

For example, an electrolytic nickel layer 6 having a thickness of about 1.5 mm is added to the upper surface 5 of the ring-shaped portion 3.

Insulation frame comprising a top 8 made of a high insulation refractory material, for example 200 mm in height, and a lower insulation, but having a higher strength and a bottom 9, for example 20 mm thick, made of a refractory material known as SiAlON. 7 is arranged above this ring-shaped portion 3, for example having a height of 40 mm.

As schematically shown in the figure, a space is formed between the nickel layer 6 and SiAlON 9, which forms an injection hole 10 having a low height of, for example, several tens of millimeters, It is led to its inner surface around the entirety of the ingot mold and is also connected to a pressurized inert gas source 110, such as argon, schematically illustrated in the figure.

The supply of the liquid metal to the ingot mold is achieved using a nozzle 11 of known type, which comprises a side opening 12 located at the level of the fire resistant frame 7, for example, near its intermediate height. do.

During casting, molten steel in a tundish, not shown, to which the nozzle 11 is attached, passes through the nozzle and its opening 12 to fill the ingot mold. The level of the free surface 13 of the liquid steel is maintained between the upper edge of the frame 7 and the opening 12, so that this opening is submerged in a liquid steel bath 2. Typically, the free surface is covered by slag 13.

As can be seen in FIG. 1, the solid steel skin 21 begins to solidify at the upper edge level of the nickel layer 6 and becomes thicker towards the bottom due to cooling by the metal walls of the ingot mold, This skin part is of course continuously renewed by solidification of the liquid steel which, in fact, continues to move downward with the withdrawal of the cast product and which comes into contact with the nickel layer 6.

The supply of pressurized argon through the injection hole 10 creates a gas fraction which is somewhat orthogonal to the inner surface of the ingot mold wall, which gas fraction is identically located at the level of the upper edge 14 of the nickel layer 6. It is used to remove the initial coagulum which may occur in contact with the lower part 9 of the frame to ensure that the skin 21 begins to solidify around the entire horizontal plane.

2 shows the change in the vertical distance d from this edge 14 to the released heat flux Φ. The solid line curve 22 shows the discharged flow rate when the ingot mold of the present invention shown in FIG. 1 is used, while the dotted line curve 23 for comparison shows that the nickel layer 6 is absent, i.e., the solid skin portion ( It shows the heat flux released when 21) begins to form in direct contact with the copper of the top 3. It can be seen that in the vertical region corresponding to the thickness of the nickel layer, the discharged flow rate decreases, and this change in flow rate can also continue several mm below the nickel layer, but by the entire ring-shaped portion 3 It does not significantly affect the total flow rate released.

3 shows a configuration variant of the ingot mold, wherein the same reference numerals as in FIG. 1 are used to indicate corresponding components. In this variant, an additional nickel layer 15 is deposited on the inner side 16 of the ring portion 3, which ring portion is pre-processed for nickel deposition, so that after such layer 15 is formed, The inner surface 17 is kept flush with the inner surface of the lower portion of the ingot mold. The thickness of the nickel layer 15 gradually decreases from the top to the bottom with respect to the height of the ring portion 3.

4 for the second variant is similar to that of FIG. 2, in which the heat flux (curve 24) emitted entirely by the ring portion is greatly reduced compared to the case without a nickel coating (curve 23). see.

FIG. 5 is a perspective view schematically showing a part of an upper portion of an ingot mold wall according to another configuration, wherein on the inner surface 32 of the ring portion 3 as shown in the enlarged scale view of FIG. 6. Vertical grooves 31 are made. The grooves 31 have a depth and width of, for example, 0.2 mm and are spaced 1.5 mm apart.

In this variant, as shown in Figure 7, the grooves are filled with a deposit 33 of a small conductive metal, such as nickel. In this case, the grooves can be spaced 2 mm apart, for example with a width of 1 mm and a depth of 0.5 mm. Nickel deposits formed in the grooves prevent the cast steel from penetrating into the bottom of the grooves. Therefore, the reduction in heat flux released in this variant is the same as that obtained by the reduction in the exchange surface proportional to the surface occupied by the grooves filled with the small conductive metal.

In order to simplify the configuration, an inert gas injection hole is not shown in FIG. 5, but it is clear that such an injection system is also preferably used in such an ingot mold.

Experimental tests conducted by the inventors show particularly satisfactory results from the metallurgical point of view of the cast product, with a reduction of more than 50% in the heat flux released at the beginning of the solidification zone, with the appearance of depressions or cracks. Products without surface defects of have been obtained for 0.1% carbon steel grades which are particularly susceptible to such defects.

The invention is not limited to only the above variations described as examples. In particular, a small conductive coating metal other than nickel may be used. In order to reduce the maintenance cost, it is desirable to achieve a reduction in the heat flux released at an upper level independent of the lower part constituting the wall of the ingot mold, but the various designs described above are only above a limited height above their upper edge. It can be used directly against the metal wall.

In addition, if the sweeping gas at the base of the frame is a "treatment" means that counteracts the local undesired coagulation effect on the fire wall of the frame during the casting product solidification process, such means is a "prevention" means of heating the frame. Can be completed by Thus, according to the invention, for example, graphite ribbons 71 which can be bent without the risk of being broken so that they can be wound around the passage of the cast metal 2 (see FIG. 9), as schematically shown in FIGS. 8 and 9. It may be effective to embed an electric heating resistor in the frame 7 in the form of (PAPYER® or SIGRAFLER®). This heating ribbon 21 may be formed in the refractory material of the frame or preferably arranged in a ring-shaped groove 72 in the frame for this purpose, for example made of two overlaps 73, 74. If care is taken to select an inert gas such as argon as the sweeping gas, the oxidation problem of the graphite heating resistor will not arise.

Claims (12)

Forcedly cooled metal wall that extends almost vertically and defines a passage of the cast metal and ensures over the entire height of the wall the release of the heat flux of the cast metal leading to the cooling and progressive solidification of the cast metal 2. In an ingot mold comprising: a continuous casting method of molten metal, in particular steel, in which the strength of the released heat flux is reduced at a level at which the metal and the wall begin to solidify in contact, An insulating frame 7 is arranged on the cooling metal wall, during casting, the free surface level of the casting metal 3 is maintained inside the frame and at the level of the frame 7 and at least at the level of its lower edge And supplying gaseous fraction to the ingot mold around the entire interface of the passageway. The method of claim 1, And the intensity of the emitted heat flux is reduced in the region of the predetermined height extending from the lower edge of the frame. The method of claim 2, And said region has a heat flux release capability that is somewhat constant over its entire height. The method of claim 2, And the region has an increasing heat flux release capability from the government toward the bottom. Metal walls (1, 3) extending substantially vertically and defining a passage of the cast metal (2) and cooling means arranged inside the wall to ensure forced cooling of the wall to a somewhat higher height; A continuous casting ingot mold, having an upper portion of the wall, provided with means for reducing the strength of the heat flux caused by the cooling means and passing through the interior of the wall, wherein the continuous casting ingot mold is disposed above the metal wall and extends upwardly. Frame 7 made of insulating material and injection means 10 for injecting pressurized gas into the ingot mold in the form of a fraction distributed around the entire boundary of the passageway at the level of the frame and at least at the level of its lower edge. Ingot mold comprising a. The method of claim 5, Said heat flux intensity reducing means comprises a metal layer (6, 15) having a lower thermal conductivity than the metal constituting the wall (1, 3). The method of claim 6, Ingot mold, characterized in that the layer (6) is arranged on the wall (3). The method according to claim 6 or 7, Ingot mold, characterized in that the layer (15) is formed on the inner surface (16) of the wall (3). The method of claim 8, Ingot mold, characterized in that the thickness of the layer (15) is reduced from the top towards the bottom. The method of claim 5, The ingot mold, characterized in that the heat flux intensity reducing means consists of a groove (31) formed in the inner surface (32) of the wall (3) while extending somewhat vertically. The method of claim 10, Ingot mold, characterized in that the groove (31) is at least partially filled with a material (33) having a lower thermal conductivity than the metal forming the wall. The method of claim 5, Ingot mold, characterized in that the electrical resistor heating means (71) is embedded in the frame (7).